water. The principal chemical disinfectants are formaldehyd gas and solution, mercuric chlorid solution, carbolic acid solution, trikresol, chlorid of lime and caustic lime, sulphur dioxid, zinc chlorid, and copper sulphate. Fire is also a most efficient disinfectant, but is applicable only for substances that are not combustible, or for combustible substances that are of little or no value. Sunlight is also an efficient disinfectant. This agent is constantly acting and, no doubt, removes most of the detrimental agents on surfaces exposed to the sun. Most bacteria grow best in the dark. Many species fail to grow at all in diffuse daylight, while direct sunlight is injurious to all species.

The Action of Sunlight Upon Bacteria, With Special Reference to Bacillus Tuberculosis.-J. Weinzirl' made a study of the various methods which have been used in determining the effect of sunlight upon bacteria. Objections are found to most of these methods in that they do not constitute true exposures, the bacteria being covered with glass or other material which absorbs and reflects some of the sun's rays. When bacteria were directly exposed to the rays of the sun without any covering over them, the author found that the germicidal action of sunlight was much more effective than it had previously been considered.

The organisms upon which observations were made were the bacilli of tuberculosis, typhoid fever, cholera, diphtheria, etc., but particular attention was given to the tubercle bacillus. It was found that this organism, as well as other pathogenic nonspore-bearing bacteria, is destroyed in from two to ten minutes by direct exposure to sunlight. According to the author, the hygienic importance of sunlight has been considerably underestimated and nonspore-bearing bacteria, when freely exposed, are killed in from one-fifth to one-twentieth of the time previously considered necessary.

Disinfection on Large Scale.-Disinfection on a

1 Jour. Infect. Diseases, May, 1907, Sup. 3, pp. 128-153, pls. 2.

large scale, for infected clothing and bedding, is usually accomplished by means of steam under pressure. A special form of apparatus is required for this purpose (see Fig. 60). A special building should be constructed for a municipal disinfecting plant. The disinfecting chamber should be so arranged that the infected clothing is brought into one room, where it is introduced into the disinfecting chamber. After it has been disinfected, it is

taken out of the chamber from the other side of a partition wall and stored in a room that has no connection with the first room except through the disinfecting chamber. The doors of the disinfecting chamber should be so arranged that only one can be opened at a time, so as to prevent infectious materials from being carried over into the room containing the disinfected clothing. The attendants handling the infected clothing should not

come in contact with those who handle the disinfected clothing. The disinfected clothing should never be returned in the same conveyance used for the collection of infected clothing.

The disinfecting power of steam is dependent upon the extent of the pressure to which it is subjected, the greater the pressure the higher its disinfecting power, because the temperature of the steam increases with the increased pressure. The steam given off from boiling water in an open vessel has the same temperature as that of the water-100° C. At one additional atmosphere pressure we obtain a temperature of 121.5° C.; at two atmospheres, 135° C.; at three atmospheres, 145° C.; at four atmospheres, 153.3° C.; and at five atmospheres, 160° C. A pressure of one atmosphere is equal to kilogram per square centimeter of surface. Spores are not destroyed when heated to the temperature of boiling water, but at a pressure of two to three additional atmospheres disinfection by steam kills spores almost immediately. All pathogenic bacteria in the vegetative stage are killed when heated to from 65° to 75° C., so that the temperature of boiling water is sufficient to kill a large number of the different species of pathogenic bacteria-the non-spore-bearing forms. When infected clothing and bedding are to be disinfected by means of steam, it is necessary to use steam under pressure to cause the heat to penetrate into the interior of the bundles to be disinfected.

Formaldehyd.-Of the different chemical disinfectants, formaldehyd is now considered the most efficient, and is in general use for the purpose of room disinfection. The disinfectant action of formaldehyd was discovered in 1886 by O. Loew. The formaldehyd gas, as generally employed for purposes of disinfection, has no great penetrating powers, and it cannot, therefore, be relied upon for the disinfection of bundles of clothing and bedding. For the disinfection of such articles the gas must be applied under pressure by means of a vacuum chamber. This

disinfectant is most commonly used for the disinfection of rooms in which there have been cases of infectious diseases. It is entirely harmless for all classes of household goods. Upon the removal of the patient the room is closed as tightly as possible, and all cracks are closed by means of gummed paper; all the bedding and clothing are spread out, the drawers, doors of cupboards, and closets are opened, and the gas is introduced through the keyhole of the door. The gas is generated in a special apparatus outside the room, either from an aqueous solution of the gas by the application of heat, by the oxidation of wood alcohol, or by the volatilization of paraform by means of heat.

Generation of Formaldehyd Gas.-An excellent form of formaldehyd gas regenerator is that manufactured by Lentz & Sons, of Philadelphia (Fig. 61), which consists of a stout copper retort of about 2 liters (4 pints) capacity, with fannel filling tube and level indicator, a stopper of special construction, and inclined brass outlet tube of large bore, connected by means of a flexible tube with another and smaller brass tube, which is inserted through the keyhole of the room to be disinfected.

The solution in the retort is heated by means of a special form of "Primus" lamp, D, which burns kerosene and develops a temperature of 1150° C. (2100° F.). The solution is introduced into the bottom of the retort through the small funnel at the top, and the stopcock A on the connection is allowed to remain open, so that exhaustion of the solution is at once detected by the escape of gas. The cap of the retort is held in position by means of a strong iron yoke, provided with a clamping screw, B. When the supply of solution in the retort is exhausted the flame is at once extinguished by turning the thumb-screw F to the left. If it is desired to continue the disinfection, a filled retort can be substituted for the exhausted one by turning the screw C, which holds the retort in place. The heat of the flame is perfectly under the control of the operator. It can be in

creased by means of the pump G, or decreased by means of the valve.

The efficiency of this apparatus is attested by the fact that the United States War Department has over one hundred of them in use, besides large numbers in use by boards of health in many of the larger cities, by hospitals, schools, and physicians.

Fig. 62 represents the Trenner-Lee formaldehyd re

generator, for which certain important advantages are claimed. It is so constructed as to permit its use either within the room to be disinfected or outside the room. The introduction of copper plates in the interior of the retort serves to prevent the frothing of the boiling fluid, and hence prevents the projection of fluid from the apparatus.